Sebacic acid is used in making Nylon 6,10 and in alkyds. Alkyl sebacates such as dibutyl sebacate, dibenzyl sebacate and polypropylene sebacate are useful as plasticizers. Sebacic esters are excellent lubricants and are much superior to mineral oil products, particularly for use at extremely low temperatures. Certain metal sebacates can be used as fungicides, stabilizers or dryers. Sebacic anhydride may be used in epoxy resins.
There are several processes known in the art for the preparation of sebacic acid. One such process based on castor oil is currently commercialized. It involves caustic decomposition of ricinoleic acid at 245.degree. C. to yield disodium sebacate and the hydrolysis of the disodium sebacate to afford sebacic acid. Several drawbacks are included in this process including high raw material coasts, the use of stoichiometric amounts of sodium hydroxide and sulfuric acid, low yield of sebacic acid (50-80%), and the production of a stoichiometric amount of 2-octanol by-product. All of these contribute to high production costs.
Another route to sebacic acid involves the oxidation of cyclodecane and produces the sebacic acid at essentially the same production costs as the castor oil process while avoiding the by-product problem.
A recent process involves a Kolbe type electrolytic dimerization of a methyl adipate salt. The main drawbacks of this process are the cost of adipic acid and the cost of energy utilized by the electrolytic process.
There is a wealth of literature relating to linear dimerization of conjugated olefins. Linear dimerization of 1,3-butadiene to octadiene or octatriene has been accomplished employing various transition metal catalysts including nickel, palladium, rhodium and platinum. Other olefins such as acrylic esters and acrylonitrile have also been dimerized to form a linear dimer employing transition metal catalysts.
The present invention is based on the discovery that sebacic acid can be prepared via the linear dimerization of methyl penta-2,4-dienoate followed by catalytic hydrogenation to dimethyl sebacate and conventional acid-catalyzed hydrolysis of the latter to sebacic acid.